When I first began this
Yes...mistake #1. Turns out that all of those little side roads can be helpful in searching out the direction of your direct path. For example, I was unable to find great grandpa on the census, until FINALLY one day he shows up living with an uncle. An uncle? What uncle? Oh...the one that I never bothered to document! Suddenly recording all of those siblings (and they had really big families back in the day!) seemed a bit more important. Simlarly, I was unable to locate where my great-great grandfather was in Illinois. I had found the woman he was married to, but it was only her and her daughters. "Well that's not right. Where's her husband? Where's her son?" Oh! The son! Searched for the son's name via the census, and in the process found great-great grandpa Allen living in the next town and his son living with him. (Apparently, grandpa and grandma didn't get along too well, ya know.)
So there ya go. Today's genealogy lesson. Don't neglect those side roads! You never know what valuable information may be drifting along in the dust.